2.doubt+賓語從句
（1）在否定句和疑問句中,doubt后面接that引導的賓語從句.例如：
I don”t doubt that he can finish the task on time.我相信他能按時完成任務.
Do you doubt that she will succeed?你懷疑她會成功嗎?
（2）在肯定句中,doubt后面一般接whether或if引導的賓語從句.例如：
I doubt whether they can swim across the river.我懷疑他們能否游過河去.
He doubts if she will keep her word.他不敢肯定她是否會遵守諾言.
注意：在肯定句中,doubt后面也可以接that引導的賓語從句,但表示疑慮較大或“不相信”.